Carboxymethyl derivatives of flaxseed (Linum usitatissimum L.) gum: characterisation and solution rheology |
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Authors: | Jun Liu Jianheng Shen Youn Young Shim Martin J T Reaney |
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Affiliation: | 1. Department of Food and Bioproduct Sciences, University of Saskatchewan, Saskatoon, SK, Canada;2. Department of Plant Sciences, University of Saskatchewan, Saskatoon, SK, Canada;3. Guangdong Saskatchewan Oilseed Joint Laboratory, Department of Food Science and Engineering, Jinan University, Guangzhou, Guangdong, China |
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Abstract: | Carboxymethyl ether moieties were introduced to flaxseed (Linum usitatissimum L.) gum (FG) by reacting gum with monochloroacetic acid (MCA). Effects of ether forming reaction conditions, temperature, NaOH concentration and molar ratio of FG (anhydroxylose equivalent) to MCA, on the degree of substitution (DS) were investigated. Treatment at 70 °C, with 7.0 m NaOH, and molar ratio of MCA to FG of 10:1 over 3 h produced a polysaccharide with a DS of 0.824 ± 0.012. Both surface morphology and thermal behaviour were modified. Solutions of FG (0.5–4.0%, w/v) exhibited shear‐thinning behaviour where viscosity decreased with decreased FG concentration. After carboxymethylation, modified polymer solutions also exhibited shear‐thinning behaviour, where dynamic viscosity was lower than that of native FG solutions at the same concentration. The dynamic viscosities were lower for solutions of modified FG with higher DS and also lower for solutions made at lower FG concentrations (0.5–4.0%, w/v). A more liquid‐like behaviour with increasing FG DS was indicated as storage modulus G′ and loss modulus G″ decreased and became more frequency dependent. The substitution of hydroxyl groups with carboxymethyl groups suppressed entanglement between FG polysaccharide chains by reducing intermolecular association. |
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Keywords: | Carboxymethylation degree of substitution flaxseed gum Linum usitatissimum L rheological properties |
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